1. Field of the Invention
The present invention refers to a filtering apparatus for house water main installations, comprising a housing having a water inlet and a water outlet, a filter bell dome removably connected to said housing, a cylindrically shaped main filter member mounted in the interior of said filter bell dome, a cylindrically shaped reversing flow filter member superposed to said main filter member and mounted in the interior of said filter bell dome, and a tubular member located in the interior of said reversing flow filter member.
In this filtering apparatus, the main filter member topped to the reversing flow filter member is flowed through from its exterior to its interior in its operative condition when the flow path through the reversing flow filter member is closed, while for backwashing the access to the outer surface of the reversing flow filter member is open and the access to the outer surface of the main filter is closed and the interior of the main filter member is connected to the outlet in said housing of the filtering apparatus by means of the tubular member located in the interior of the reversing flow filter member such that the water to be filtered flows through the reversing flow filter and then partially through the outlet of the filtering apparatus to a consumer's installation and partially through the main filter member from its interior to its exterior.
2. Prior Art
Such a filtering apparatus which can be cleaned by reversing the flow of water through the filter member is known from e.g. Swiss Patent Nr. 603,213. The filtering apparatus disclosed in said Swiss Patent comprises as obstruction mechanism in the reversing flow filter member. The obstruction mechanism being in its open condition, the water flows through the reversing flow filter and contaminated water flows out of the filtering apparatus via a valve which is opened during the reversing flow operation. Thereby, the problem of a continuous water supply from the filtering apparatus even during the cleaning operation was solved: For cleaning the filter member in counterflow only a part of the water supplied to the filtering apparatus is used, while the remaining part of the water bypasses the main filter member and flows directly to the outlet of the filtering apparatus. Thus, filtered water is also obtained during counterflow cleaning of the filtering apparatus.
The main disadvantage of this filtering apparatus is that the contaminated main filter member is only hydraulically cleaned in counterflow while the reversing flow filter member is not cleaned at all. However, it often happens that during backwashing, depending on the water pressure, the deposits on the main filter member initially are removed only at a certain place on the outer surface of the main filter member with the consequence that the entire cleaning water flows through the opening created in this way. Thus, the main filter member is not properly cleaned and a layer of deposits and contaminations remains on the main filter member after switching to normal operation of the filtering apparatus. Such a layer of deposits and contaminations impairs the proper operation of the filtering apparatus.
Tests run by the Inventor have shown that a thorough removal of deposits and contaminations from the surface of the main filter member is not possible solely by hydraulic backwashing. The layer consisting of deposits and contaminations has irregular thickness and only the weakest parts of this layer are removed during backwashing while the remaining major layer of deposits and contaminations is kept on the main filter surface.